Optical coupler

ABSTRACT

A semiconductor photonic device includes a substrate, facet(s), and optical coupler(s) associated with the facet(s). Each optical coupler can couple an electromagnetic field incident on the respective facet towards the substrate as the electromagnetic field proceeds into the semiconductor photonic device. In some examples, each coupler has waveguides extending in a longitudinal direction and at least partly encapsulated within corresponding cladding layers. A first waveguide extends farther from the facet in the longitudinal direction than does a second waveguide. The second waveguide is located farther above the silicon substrate than is the first waveguide. The coupler can include a stack of waveguide assemblies. A lower waveguide assembly can include one waveguide. An intermediate or upper waveguide assembly can include multiple waveguides. In some examples, at least one waveguide tapers along its length.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a nonprovisional application of, and claims priorityto and the benefit of, U.S. Patent Application Ser. No. 62/383,145,filed Sep. 2, 2016 and entitled “Optical Coupler,” the entirety of whichis incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, features, and advantages of various aspects will become moreapparent when taken in conjunction with the following description anddrawings. Identical reference numerals have been used, where possible,to designate identical features that are common to the figures.

FIG. 1A shows a front view of an Si inverse taper without claddedwaveguide.

FIG. 1B shows a top view of an Si linear inverse tapered waveguide.

FIG. 1C shows a front view of an Si inverse tapered, cladded waveguide.

FIG. 1D shows examples of waveguides.

FIG. 2A shows a front view (left) and a top view (right) of a triple armSiN chip-edge optical coupler.

FIG. 2B shows further details of FIG. 2A.

FIG. 3 shows results of a simulation of the electric-field magnitude ofelectromagnetic radiation of the (top row) TE₀₀ mode or (bottom row)TM₀₀ mode, at positions z=0, z=L₀, z=L₁, and z=L₂ (respectively fromleft to right) along the longitudinal axis of an example optical couplersuch as that shown in FIGS. 2A and 2B.

FIG. 4A shows a top view of an example optical coupler includingdisplaced waveguides.

FIG. 4B shows EME simulation results of mode conversion efficiency ofthe design in FIG. 4A, with L0=100 μm, L1=800 μm, and L2=400 μm.

FIG. 5 shows a front (facet) view of an optical coupler using a 3×4 SiNtip matrix.

FIG. 6A shows top views of layers of an example optical coupler,including a top SiN layer (above) and Middle & bottom layers (below)that have an intermediate dual SiN taper.

FIG. 6B shows further details of FIG. 6A.

FIG. 7 shows top views of a stage 3 optical coupler design with (left) 3section and (right) 4 section piecewise linear shape, including straightSiN and tapered Si.

FIG. 8A shows another example of a stage 3 optical coupler design havinga buffering region.

FIG. 8B shows further details of FIGS. 7 and 8A.

FIG. 9 shows simulation results indicating the magnitude of the electricfield in an example optical coupler at Z=0 for TE illumination.

FIG. 10 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=0 for TM illumination.

FIG. 11 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=0.5 L₀ for TEillumination.

FIG. 12 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=0.5 L₀ for TMillumination.

FIG. 13 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀ for TEillumination.

FIG. 14 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀ for TMillumination.

FIG. 15 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀+0.5 L₁ for TEillumination.

FIG. 16 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀+0.5 L₁ for TMillumination.

FIG. 17 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀+L₁ for TEillumination.

FIG. 18 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀+L₁ for TMillumination.

FIG. 19 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀+L₁+0.5 L₂ for TEillumination.

FIG. 20 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀+L₁+0.5 L₂ for TMillumination.

FIG. 21 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀+L₁+L₂ for TEillumination.

FIG. 22 shows simulation results indicating the magnitude of theelectric field in an example optical coupler at Z=L₀+L₁+L₂ for TMillumination.

FIG. 23 is a high-level diagram showing the components of adata-processing system.

FIG. 24 is an end (facet) view of an example optical coupler.

FIG. 25 is a top view of an example waveguide in an example opticalcoupler.

FIG. 26 shows results of a simulation of the electric-field magnitude ofelectromagnetic radiation of the (top) TE₀₀ mode or (bottom) TM₀₀ mode,at various positions along the longitudinal axis of an example opticalcoupler such as that shown in FIGS. 5-6B.

FIG. 27 is an axonometric drawing showing internal components of asilicon photonic device, and related components.

The attached drawings are for purposes of illustration and are notnecessarily to scale.

DETAILED DESCRIPTION

Steps, operations, or features of various methods described herein canbe performed in any order except when otherwise specified, or when datafrom an earlier step is used in a later step. Example method(s)described herein are not limited to being carried out by componentsparticularly identified in discussions of those methods. Throughout thisdiscussion, a term has the same meaning whether it is presented with orwithout subscripts (e.g., “SiO2” is the same as “SiO₂”), unlessotherwise indicated.

FIGS. 1-8B show example configuration of optical couplers according tovarious aspects, and simulation data. FIGS. 9-22 show results ofsimulations of electromagnetic fields at various points along thedirection of propagation of light through example couplers according tovarious aspects. As used herein, the terms “light” and “optical,” andsimilar terms, are not restricted to the visible range. “Light” refersto electromagnetic radiation of whatever wavelength. Some examplescouplers herein have waveguide and layer dimensions permitting effectivecoupling of at least one of the following ranges or bands of wavelengthsof light: infrared (e.g., ˜750 nm-˜1 mm, near-infrared, far-infrared,visible (e.g., ˜400 nm-˜700 nm), ultraviolet, telecommunications (e.g.,˜1260 nm-˜1675 nm), or specific telecommunications bands (e.g., the“1310 window,” ˜1260 nm-˜1360 nm, the “1550 window,” ˜1530 nm-˜1565 nm,or ˜1520 nm-˜1620 nm).

Some examples include method(s) of manufacturing couplers. Suchmethod(s) can include performing SOI CMOS fabrication processes, e.g.,including deposition, masking, etching, or planarization steps, in anycombination, to provide structures such as those described herein.

Various examples relate to an edge coupler for standard single modefiber based on SOI substrate. Some example couplers include multipleinverse tapers (taper matrix) to guide optical mode during modeevolution, e.g., as discussed herein with reference to FIGS. 5-6B.

Si optoelectronics and photonic devices are increasingly popular. Tocommunicate between such devices on chip, Si chips performing photonicprocessing couple light in and out of optical fibers. An example of sucha fiber is CORNING SMF-28, designed for use in the λ=1310 nm window andthe λ=1550 nm window commonly used in telecommunications. SMF-28 has amode-field diameter of 9.2±0.4 μm at 1310 nm and of 10.4±0.8 μm at 1550nm. However, Si devices require very small cross-sections, e.g.,0.25-0.5 μm in width and height. This is much smaller than mode-fielddiameter (e.g., approximately the core size) of optical fibers (e.g., ˜9μm). Therefore, a great deal of light is lost in a butt-coupling, e.g.,from 9 μm diameter to 0.25 μm×0.5 μm. There is a need for a low-lossfiber-to-silicon light coupler.

Silicon inverse nano-tapers are promising as fiber-to-chip edge couplersdue to the perceived advantages of broadband performance and the ease ofon-chip integration. Earliest developed Si inverse taper is developed byLipson's group as shown in FIG. 1A and FIG. 1B, where Si taper 3 isembedded in SiO₂ 2. Top view shows taper width expands linearly from tipwidth W_(tip) up to W_(wg) (usually 450 nm for single mode Si waveguidewith H=220 nm) in a length of L_(taper). For taper fabricated on a SOIwafer, there is always a buried oxide (BOX) layer to avoid power leakagefrom waveguide 4 to Si substrate 1. Since most commercially availableBOX has thickness less than 3 micrometers, hence this conventionalinverse taper does not suit for standard cleaved fiber (SMF-28) withmode field diameter (MFD) (1/e² power diameter in a Gaussian profile)around 10 μm. A solution is to used lensed fiber to focus beam at tapertip such that input mode with strongly reduced size no longer sufferfrom leakage. Another alternative is to deploy tapered fiber core toachieve mode size reduction yet both techniques have not yet become asolution for industry due to its higher costs and significantlyincreased alignment and packaging challenge.

There are several design guidelines shared by designers when working oninverse taper embedded in SiO2 background. First and foremost, sincethere is no total internal reflection to trap the injected beam, the tipwidth at the facet should be carefully designed to trap the injectedbeam immediately at arrival. This request the facet cross-sectionsupport TE₀₀ and TM₀₀ mode with decent overlap with input Gaussian mode,although some mode mismatch loss at facet is introduced. Another idea ismode transition loss scales up with input MFD while down with taperlength. Mode conversion efficiency can be strongly enhanced when modecenter is aligned with Si taper.

In fact, even if bottom Si substrate is replaced by index matchingmaterial (no more leakage) with great effort, inverse taper based edgecoupler still does not serve as good solution for SMF-28. An intuitivechallenge is large input MFD requires excessive taper length to reducetransition loss even if mode is aligned with Si taper. Another problemis the birefringence introduced at tip coupling. In order to match with10 um MFD input Gaussian mode, tip width has to be pretty narrow for 220nm thick Si wafer. As taper tip is away from square shape, supportedTE₀₀ and TM_(00 deviates) from each other meaning decent mode overlap atfacet cannot be reached for both TE and TM polarizations. In at leastone example, with discontinuous taper at subwavelength scale, tip can bedesigned as square shape to match both polarizations. With discontinuousmetamaterial taper, 1.3 dB loss can be obtained for SMF-28 fiber,although suspended structure with index matching material filling is notan industrialized manufacturing process.

An alternative design of edge coupler for large MFD fiber is to clad anintermediate waveguide on top of Si taper, as shown in FIG. 1C. Thewaveguide has refractive index higher than that of BOX to confine theinjected beam and its dimension supports fundamental mode overlappingnicely with input beam with huge MFD from standard cleaved fiber. HereW_(tip) becomes trivial since mode is initially guided in intermediatecladded waveguide 5 when taper width is too narrow to guide. Given thesame top view in FIG. 1B, W_(tip) should be as narrow as possible toreduce overlap and index mismatch in order to achieve decent tipcoupling efficiency. Such design however unavoidably causes verticaldisplacement between input beam and Si taper, rendering evanescentcoupling much less efficient. In addition, only polymer material (suchas SU-8) can become CMOS compatible candidates for intermediatewaveguide, nonetheless organic polymer is not seen as reliable as SOIfor commercial applications. In addition, multi-mode cladded waveguidecan also lead to multimode-interference (especially given inputmisalignment), which can be undesirable.

Various examples include edge coupler on SOI platform without claddedwaveguide meanwhile does not rely on Si substrate removal or indexmatching material filling. The solution is compatible with standard CMOSfabrication process and offers desirable tolerance to index variations.

Example embodiments involve the tip design at facet. For SMF input, modecan be trapped at several microns on top of BOX layer to reduce leakagetowards substrate. This can be done with initially depositing thick SiO₂first before building taper layer and ultimately covered with SiO₂ topcladding. The taper material can be (but not confined to) SiN (e.g.,SiN_(x), such as stoichiometric Si₃N₄, or other forms of siliconnitride) and amorphous Si. For trapping a large optical mode with lowbirefringence, high overlap, and robustness to index variations,multiple tips (e.g., in a matrix) can be used.

FIGS. 1A-1D illustrate a prior scheme, and shows a front view of an Siinverse taper coupler without a cladded waveguide. Vertically, thewaveguide is constant-thickness. Examples are single-mode. In FIG. 1D,the note “light is squeezed out” refers to the fact that, aselectromagnetic radiation progresses leftward and the tip widthdecreases, the amount of the electromagnetic energy carried in the Sicore decreases (and the opposite for light moving from left to right).

FIG. 1B shows a top view of the Si linear inverse taper of FIG. 1A. Inprior schemes, a light source, e.g., an optical fiber, is to the leftside of FIG. 1B, and light can propagate from left to right. In area 3,cross-section (mode field diameter) expands. Expanded mode is about thesame size as an optical fiber core. In area 4, the width is about 0.45μm, so the light is confined.

However, structures as in FIG. 1 are limited by commercialsilicon-processing limitation. For example, commercial-grade BOX is atmost 3 μm thick, which limits the mode field width. Light that couplesto the Si substrate will be lost. Therefore in order to reduce leakagetowards substrate, the core of initial receiving waveguide is elevated.

FIG. 1C shows a prior scheme in which the fiber mode couples to thecladded waveguide and then is confined to within the taper. As the Siexpands along the direction of propagation, the field is sucked into thecore. The cladding can be made very large, e.g., the same size as thefiber mode. However, a large enough waveguide such as in FIG. 1C is amulti-mode guide, not a single-mode guide. Therefore, fiber misalignmentcan cause multi-mode interference because not only the fundamental mode,but also higher-order modes, of the waveguide will be excited. Thisresults in coupling loss.

FIGS. 2A-2B show an example configuration of an optical coupler. Variousexamples can be used with photonic or electro-optical devices, e.g.,active units 2322, FIG. 23. Various examples of couplers can be used forany situation in which a change of mode field diameter is required, orin which the distance between the optical axis and a silicon (or otherhigh-index) substrate has to be adjusted. Various examples can be usedwith non-silicon devices, e.g., III-V devices.

The left halves of FIGS. 2A and 2B show the view with light propagatingfrom the fiber into the device into the plane of the figure. The righthalves show three separate top views that can be stacked to show thefull top view. In some examples, waveguides in the middle (N2) andbottom (S0) layers are tapered.

As shown in FIGS. 2A and 2B, one embodiment of the design (called triplearm SiN edge coupler) includes triple SiN tips at 5 um above BOX (layerN1). One layer of multiple SiN tips (N1, three tips in this embodiment)with 300 nm thickness is deposited to trap the incident beam assumingaligned with beam center. In some examples, each individual waveguide inN1 has a substantially constant width, e.g., 300 nm thick×160 nm wide.With 160 nm tip width and 1.8 μm center-to-center spacing, 92% TE and90.5% TM facet coupling efficiency can be achieved with input fiber modewith 10 μm MFD. Similar to ‘trident spot-size converter’, triple arm SiNtips strictly support single mode hence multimode problem caused byinput misalignment can be reduced or eliminated. The guided mode howeveris very weakly guided with some leakage. To solve the problem, tipspacing are gradually reduced to better confine the incident beam, withincreased effective index (Neff) and reduced mode size. In someexamples, N2 is omitted, and only N1 and S0 (Si) layers are used.

At 1.5 um above BOX layer, there is also an intermediate SiN Layer (N2)which only appears L0 distance into the facet. Then mode located attriple arms can vertically coupled to the intermediate SiN taper andultimately coupled to Si taper (layer S0) as shown in FIG. 3.Intermediate SiN taper in layer N1 serves as a stepping-stone orintermediate coupling step layer that make the mode smaller and closerto Si taper in layer S0. Without intermediate SiN layer, direct modecoupling from triple arms in N2 down to Si taper in S0 can be performedusing a longer Si taper, e.g., 2×, 3×, or longer compared to the lengthof the Si taper in S0 when using an intermediate waveguide (e.g., inN2). Compared to some prior schemes, example configurations can achievethe same functionality but on one SOI wafer alone, avoiding multiplewafer bonding steps. Various examples of waveguide arrangements shown inat least FIGS. 2A and 5 permit drawing the optical mode of incidentradiation from the larger diameter of the fiber down towards thesubstrate and into the smaller waveguide (or vice versa, for emission).

In some examples, intermediate SiN taper, e.g., in the L1 region, worksas a stepping-stone for evanescent coupling. The introduction of Si tipat L1/L2 interface does not cause significant mode mismatch loss.Spacing the intermediate SiN layer apart from the Si layer or increasingthe width of the intermediate taper can help avoid increasing modemismatch loss. In some example, a 400 nm wide waveguide 1.5 μm above theSi taper can provide less than 0.05 dB mismatch loss. Simulation resultsshow that, when top layer tip center-to-center distance is reduced from1.8 μm to 1.2 μm with 100 μm long L₀, 96% power transmission can beachieved at 700 μm taper length for both polarizations.

Throughout this document, terms such as “top,” “middle,” “bottom,”“above,” “below,” “over,” and “on top of,” when used with respect tolayers or structures in those layers, describe relative positions ofthose structures or layers, without regard to the orientation of thedevice or structure containing those structures or layers. For example,in FIGS. 2A and 2B, layer S0 is over the Si substrate; layer N2 is overlayer S0 and the substrate; and layer N1 is over layer N2, layer S0, andthe substrate. This is the case even if the chip including layers N1,N2, and S0, and the substrate, is turned upside-down or on edge.

CMOS processing can effectively produce ICs or other components thathave multiple planarized layers. CMOS processing can provide precisecontrol of film thickness (vertical) and waveguide widths (lateral).However, in the back-end-of-line (BEOL) process, films are required tobe deposited at low temperatures (<400° C.) to avoid disturbing thedopant profiles. For example, SiN and SiO₂ are deposited by PECVD, whichcan lead to large variations in refractive indices. However, to increasethe optical Mode field diameter (MFD), the refractive indices of thecore and cladding are preferably close together, similar to thesituation of optical fiber (e.g., Δn<0.02). Small variations of materialindices will cause large MFD changes, affecting the coupling efficiency.Some schemes use nano tapers and metamaterial tapers, but those requirehigh resolution lithography control, not generally compatible with CMOSprocessing, to match MFD of 10 μm. By contrast, various examples hereinguide the light using structures that can be produced withouthigh-resolution lithography, and that provide refractive indextolerance.

FIG. 3 shows example simulated mode profiles for the configuration ofFIGS. 2A and 2B. The columns are numbered I-IV for ease of reference.The N1 and N2 layers (as shown in FIGS. 2A and 2B) are labeled withdotted lines. In a TE mode (top row), the E field is oscillatinghorizontally. In a TM mode (bottom row), the E field is oscillatingvertically. Fiber has circular symmetry so doesn't distinguish TE fromTM. Therefore, light coming in from the fiber may have any angle oflinear polarization. However, for a coupler without circular symmetry,such as the structure shown, TE and TM differ in behavior. Therefore,when light from the fiber reaches the coupler, the light can bedecomposed into TE and TM components (e.g., for purposes of analysis, orby structures in the coupler). Various examples have couplingcoefficients substantially the same for TE as for TM, thus permittingeffectively coupling incoming light from the fiber to the siliconwaveguide (S0) regardless of the polarization angle of the light in thefiber. In the illustrated example, the input beam initially couples to asupermode at the tip arrays at the facet, then couples to theintermediate step (N2), and finally couples to the Si layer S0. With 300nm thick triple SiN tips of 1.8 mm spacing, 160 nm tip width, and a 7 μmtop cladding, facet coupling efficiency can reach 92% for TE and 90% forTM. This example also provides tolerance to misalignment: over 70% tipcoupling efficiency for 1.5 μm misalignment in both x and y directions,in both TE and TM.

The vertical positions of intermediate SiN Layer N2 can be optimized fordifferent design guidelines. The mode evolution is achieved in twoparts: firstly coupling from triple arms to intermediate layer andsecondly from intermediate layer down to Si layer. When verticallycloser to triple SiN arms, first part increases in efficiency while thesecond part decreases in efficiency. In some embodiments, theintermediate layer is vertically closer to Si layer in order to reduceSi taper length. This is due to the consideration that Si/SiO2interfaces can suffer scattering loss orders of magnitude higher thanSiN/SiO2, as discussed below. Hence some examples trade Si taper lengthwith SiN length in order to suppress accumulated scattering loss.

When light arrives from the fiber, the light initially only interactswith the three upper SiN nitrides (N1). N1 is ˜8 μm above the Sisubstrate. Center of fiber is aligned with center of N1 in someexamples. As the three nitrides approach each other, the mode profileshrinks because the high-index cores are closer together.

If only one waveguide were used (300 nm×160 nm wide), the light wouldnot be effectively combined. In some examples, two waveguides are used,each with a wider width than 160 nm.

By the time the light reaches the L0 interface, the mode has shrunk.However, there still a need to shift the center of the field (theoptical axis) vertically towards the Si substrate, e.g., to move thelight down by ˜5 μm.

Therefore, the N2 waveguide is used. There is a taper on the N2waveguide. In some examples, for the Nitride 2 (middle nitride), the tipwidth can be ≤80 nm, and can be linearly tapered to a final width of˜400 nm. The total taper length for the middle nitride waveguide can be,e.g., 800 μm.

FIG. 3, column II, shows how the field has shrunk due to the initialmerging of the N1 waveguides towards each other. The N2 waveguideexpands horizontally, but not in thickness, in this example. The lighttravels in both N1 and N2. As the N2 waveguide expands, lightredistributes from N1 to N2. In some examples, the N1 waveguides canshrink as the N2 waveguide expands. In other examples, e.g., FIGS. 2Aand 2B, the N1 waveguides can have a substantially constant widthbetween L0 and L0+L1. N2 has a higher capability to confine the light asit widens, compared to the N1 array. In some examples, e.g., forsimulations illustrated herein, e.g., in FIG. 3, the refractive indicesfor Si, SiO2, and SiN are ˜3.47, ˜1.444, and ˜2.0, respectively.

Other examples of simulations at various points along the direction ofpropagation of the light are shown in FIGS. 9-22. FIGS. 9-22 show X-Yslices at various points along the Z axis, using dimensions L0, L1, andL2 as in the configuration of FIGS. 2A and 2B.

In column III, the optical axis is along the N2 waveguide.

In column IV, the optical axis is along the Si. The refractive index ofSi is greater than the index of SiN, so light transfers from middle tobottom. The field is an evanescent-field transfer. Substantially all ofthe optical power becomes concentrated in the Si waveguide, in someexamples.

In some examples, e.g., as in FIGS. 2A and 2B, right half, the N2waveguide(s) can have substantially constant dimensions as the Siwaveguide expands. In some examples, e.g., as in FIGS. 6A and 6B, the N2waveguide(s) can taper out as the Si guide expands.

The coupler can be connected to muxes, demuxes, modulators, detectors,or other components. Examples are discussed herein, e.g., with referenceto FIG. 23, active unit 2322.

Some examples include N1 and Si, but not N2, waveguides. The evanescentfield decreases exponentially with distance. If no N2, the Si taper canbe longer along the direction of propagation—a more gradual taper. Insome examples, any number of nitride layers can be used. In someexamples, the coupler can be, e.g., 100 μm-200 μm long, or <2 mm long.

Some examples are configured to reduce mode mismatch loss at interfacesbetween stages. At the L0/L1 interface, intermediate layer tip widthless than 80 nm can make render mode mismatch loss negligible. At L2/L1interface, width of intermediate taper of 300 nm is able to trap themode well enough that removal of triple arm will not lead to any powerloss. Also Si taper width less than 80 nm can provide that the mode isstill well confined in SiN without affected by Si tip. In some examples,using a wide tip introduces an abrupt change in optical characteristicsat which mode loss can occur. In some examples, in N2, tip width <80 μmleads to negligible mode mismatch loss. Similarly, narrow tips in Si canreduce mode mismatch loss.

FIG. 4A shows an example coupler. To reduce the Si taper length, apiecewise-linear (PWL) taper with three section width expansion (tipwidth 60 nm→120 nm, 120 nm→200 nm transition, 200 nm→450 nm transition)is shown. The middle section takes ⅔ of Si taper length, and the initialtaper and the final taper are ⅙ of the length each. Based on adiabaticmode transition, the device offers acceptable misalignment tolerance, sothe intermediate SiN waveguide does not have to be exactly aligned withSi. There can also be displacement introduced in the design in order toavoid planarization steps in processing.

FIG. 4A shows an example design with displacement introduced, whereL0=100 μm, L1=800 μm and L2=400 μm. FIG. 4B shows simulated broadbandmode transition loss calculated by EME method (eigenmode expansionmethod), which shows at least 93% mode conversion efficiency for bothpolarizations. In some examples, PWL has a higher mode conversionefficiency than a straight taper at the same taper length. Modetransformation is most intense in the middle section, which expands from120 nm to 200 nm, which is why the middle section is the longest. Someexamples use a 450 nm industry-standard waveguide for single-modeoperation in λ=1.5-1.6. Some examples use a waveguide thickness of 200nm.

In some examples, e.g., FIGS. 2A-3, the N2 waveguide can be verticallyaligned with the Si waveguide, e.g., the N2 waveguide and the Siwaveguide can be spaced apart along a line parallel to the Y axis. Insome examples, e.g., FIG. 4A, the N2 waveguide can be laterally offsetfrom the Si waveguide, e.g., in the ±X directions. In the example ofFIG. 4A, the N2 waveguide is laterally offset, and the device isoperational. Moreover, some examples using lateral offset can befabricated using planarization processes having relatively relaxedtolerances compared to examples using vertically aligned waveguides.This can permit manufacturing such devices less expensively. Lateraloffset can be present between any layers. FIG. 4A shows lateral offsetin the labeled X direction, but lateral offset can additionally oralternatively be present in the Y direction. Devices can be designed tooperate as desired in the presence of characterized fabrication-processX or Y tolerances, or other tolerances.

Additional losses can include scattering loss and leakage throughsubstrate. Scattering loss can be due to roughness on the sides of thetapers. Both losses can be estimated by staircasing approximation thataccumulated loss equals to summation of loss from each individualpropagation step (1 μm for example). For an example of the illustratedgeometry with 5 nm σ_(RMS) sidewall roughness, accumulated scattering isestimated as 0.18 dB for TE and negligible for TM while SiN taper'sscattering loss can be negligible. Leakage cannot be neglected as wellsince there is no total internal reflection anymore to guide the mode.Si stage leakage is estimated as 0.2 dB for TM and 0.1 dB for TE, withsimilar amount of accumulated leakage after first two stages. Combingall sources of loss together with 0.45 dB coupling loss at facet, totalfiber to chip loss for both polarization is within 1.3 dB per facet. Insome examples, the coupler is as short as possible to reduce loss due tosurface roughness. In some examples, the Si taper is shorter than theSiN. The SiN embedded in SiO2 has reduced scattering loss, becausescattering loss is positively correlated with index difference, andn(SiN) (refractive index n of SiN) is closer to n(SiO2) than is n(Si).

In some examples, SiN taper scattering loss is negligible since SiN/SiO2has almost 2 orders of magnitude lower scattering loss in dB thanSi/SiO2. In some examples with σrms=10 nm and a 400 μm-long taper, alinear taper can provide 2.2 dB TE loss and 0.2 dB TM loss, and anonlinear taper can provide 0.77 dB TE loss and 0.1 dB TM loss. In someexamples, scattering loss scales with σ_(rms) ². Therefore, a devicehaving σ_(rms)≤5 nm can have ≤0.19 dB scattering loss for TE and ≤0.025dB for TM on a nonlinear taper. In some examples, TE leakage is lowerthan TM. In some examples, a mode transition of the TM component appearsearlier along propagation direction (lower z position) than of the TEcomponent. An example 400 μm-long nonlinear Si taper can have leakage of0.31 dB for TM and 0.13 dB for TE. The L1 section can also have leakage,so total leakage can be 0.6 dB for TM and 0.3 dB for TE. Includingscattering loss and leakage loss through Si substrate, an example canhave TE leakage: 0.3 dB, TM leakage: 0.6 dB, TE scattering: 0.19 dB, TMscattering: 0.025 dB, resulting in total TE loss: 1.05 dB per facet andTotal TM loss: 1.3 dB per facet.

Some examples are broadband. For example, as shown in FIG. 4B, a 100-nmbandwidth is available. Dimensions can be adjusted, e.g., the 450 nm ofFIG. 4A, based on the wavelength of interest. In an example, a devicewas tested and found to be operative across a bandwidth from λ=1520nm-1620 nm. This includes the typical telecommunications range used foroptical fibers. Examples can additionally or alternatively be used inthe 1310 nm band, other infrared bands, visible bands, ultravioletbands, or other electromagnetic spectrum bands.

FIG. 5 shows another embodiment of a design including a 3 by 4 SiN tipmatrix to guide the injected beam, with parameters given in FIG. 5. Withmultiple layer of SiN tip arrays, fundamental mode profile can bedesigned to provide effective overlap with fiber mode. The matrix can bedesigned to improve total coupling efficiency while reducing couplerlength, and thus losses due to roughness, e.g., as discussed above.

In FIG. 5, a matrix is used for initial mode confinement. An exampleconfiguration anchors the mode to be substantially circular rather thansubstantially elliptical, which can reduce losses when the circularfiber mode couples into the waveguide. The array in N1U, N1M, and N1Lcan be sized to match the diameter of the input fiber. In some examples,n(SiN) and n(SiO2) can be different from a value used in simulating thestructure, e.g., due to process variations, and the device can stillfunction. n(Si) is generally constant because the Si is pure andmonocrystalline. However, n(SiN) and n(SiO2) vary depending ondeposition method. Using a matrix of SiN waveguides, the mode is spreadover the matrix. Therefore, the mode is less affected by n variations inany one waveguide.

FIG. 5 shows two waveguides in N2, though any number can be used. Insome examples, there can be any number of nitride layers between thematrix and the silicon.

In some examples, the matrix layers can be readily fabricated becausethe individual N1 segments are relatively thin. For example, usingmatrix N1 layers thinner than the N2 layers can permit fabricating arelatively large number of matrix layers without excessive cost, whilestill providing effective mode transfer via the N2 layers to the siliconwaveguide.

Single mode optical fiber can support a MFD=10 um because of its lowclad-to-core index contrast (e.g., Δn<0.02 between the cladding and thecore). However at low index contrast, the effect of index control uponmode size variation becomes quite significant. Some examples of couplersare designed to behave in similar ways to fiber (e.g., low indexcontrast), in order to match modes with fiber modes and reduce loss atthe fiber-coupler interface.

In the example of FIG. 5, and also FIGS. 6A and 6B, the illustrated tipmatrix includes very thin SiN (core) layers stacked, so the matrixoccupies a relatively small volume. The low percentage SiN in the faceof the matrix, e.g., the facet of the coupler, means that the refractiveindex in the coupler at the fiber-facing surface is just above thebackground index of SiO₂, so the structure exhibits low index contrastsimilar to that of optical fiber. In addition, in some examples, the tipmatrix can support an almost circular mode rather than elliptical modes.The circular mode shape matches better with fiber modes than would anelliptical, flat, or rectangular mode shape, further reducing couplingloss.

FIGS. 6A and 6B show an embodiment of the design in which three layersof identical SiN tips are deployed with 2 um vertical spacing. Dimensionof SiN tips are 300 nm wide and 100 nm thick, horizontally spaced by 1.5μm. This is a nonlimiting example, and other dimensions can additionallyor alternatively be used. As multiple SiN layer deposition is involvedduring fabrication, thickness of SiN tips is designed as thin enough(100 nm for example) to avoid planarization steps. FIGS. 6A and 6B showa top view of layers N1U, N1M, N1L, and N2 of FIG. 5. The upper plot inFIGS. 6A and 6B shows N1U; the lower plot shows N1M, N1L, and (at right)N2. The “Si here” arrow points in the longitudinal direction of thecoupler, e.g., towards an active unit 2322.

Referring to FIGS. 5-6B, in some examples, at the facet, only a matrixof 3×4 SiN tips (300 nm wide and 100 nm thick) is exposed to receiveincident radiation. The embedded SiN waveguides may not be able to guidethe light individually, but collectively they form an almost single modewaveguide with a mode field diameter ˜10 μm. After a distance L1 intothe edge, a pair of 300 nm thick SiN inverse tapered waveguides begins.After another distance of L2, an Si inverse taper begins. The 3×4 SiNtips expand and pin the MFD to ˜10 μm. Using a matrix of tips, the modeshape is anchored and is more robust against index variation than someprior schemes. For example, between 1500 nm and 1600 nm in an example,tip coupling efficiency is above about 95% for n=2±0.1 for SiN andn=1.45±0.05 for SiO₂. In most simulated examples of this design, TEefficiency >96% and TM efficiency >98%.

In N1U, the SiN waveguide reduces in width as the light travels left toright. Therefore N1U has reduced confinement capability, so forces themode down to N1M and N1L. N1M and N1L have the same shape of SINwaveguides.

In some examples, the N2 nitrides increase in width as the N1M and N1Lnitrides decrease in width. This moves the mode down to N2. In someexamples, N1U tapers out and then N2 starts at the same pointleft-to-right.

In some examples, N1U can be used in place of N1 in FIGS. 2A and 2B, orvice versa. In some examples, FIGS. 2A and 2B N1, or N1U, M, or L inFIGS. 6A and 6B, can have any number of waveguides.

Such 3 by 4 SiN tip matrix can support TE₀₀ and TM₀₀ that overlap withfiber mode more than 98%, which is more than be achieved within onelayer of multiple tips alone. Another advantage is that such modecoupling becomes fairly robust against index variation. With SiN andSiO2 index variation of 0.1, more than 95% coupling can still beobtained. Similar to previous embodiments, TM modes can experiencerelatively higher leakage while TE modes experience relatively higherscattering loss due to sidewall roughness. Couplers can be designed,e.g., as with examples herein, to balance the TM leakage and TEscattering loss.

Mode evolution of tip matrix provides flexibility in designingstructures. Leakage suppression for example can be done by reducinghorizontal gaps or widening SiN tips. This is accompanied by incrementof effective refractive index (Neff) and mode localization. Modeshifting downwards can be achieved by tapering out SiN layers from topto bottom layer by layer. As top layer mode localization is graduallydecreased, the layer beneath can gradually increase mode confinementcapability to trap the down-shifted mode. Example simulations are shownin FIGS. 9-22.

One embodiment of triple layer SiN arrays is shown in FIGS. 6A and 6B.For the top SiN layer, width of SiN tapers down to 100 nm to squeeze themode downwards. Meanwhile middle and bottom SiN layers reduce horizontalgaps to zero. After this stage of mode evolution, mode size is reducedand position shifted downwards.

At start of stage 2(left end of “L2” arrow), top layer of SiN matrix candisappear due to absence of mode localization since mode is onlyconfined at middle and bottom SiN layer. An additional SiN layer (300 nmthick) is introduced here at 1.5 um on top of Si taper as intermediatecoupling step. An embodiment is to use dual SiN taper with expandingwidth to trap the mode down to intermediate layer.

Evanescent coupling shows a common trait that TM mode is more weaklyconfined hence coupling is more efficient than TE but also suffershigher leakage. During evolution, mode will experience a leakage peak atposition where mode is most efficiently coupled down. Mode couplingprocess becomes most efficient during narrow range (window) of geometrychange, e.g., tip-width change, while leakage peaks exactly at thiswindow. Hence combination of both loss can be mathematically minimizedor otherwise reduced at a certain length of stage 2. For example whendual Si taper (1.6 um horizontally center-to-center spaced) widthexpands from 100 nm to 500 nm, stage 2 length optimized at around 500 umfor TM with 0.3 dB total loss.

In the area before the silicon (left of “Si here” arrow base), TE(E-field oscillations in the wafer plane) and TM (E-field oscillationsperpendicular to the wafer plane) behave similarly. However, TE and TMtransfer differently from N2 to Si. Some examples are designed toprovide increased efficiency for TE compared to TM, or vice versa.

In some examples, the tips of the matrix waveguides can be offset fromeach other in Z, e.g., increasingly to the right as you move down thestack towards the substrate.

FIG. 7, left side, shows an example taper that can be used to the rightof the portions of the coupler shown in FIGS. 6A and 6B. Last stage isthe mode coupling from dual SiN waveguide down to Si taper. Si taperhence can be designed as piecewise linear as shown in FIG. 7 (similar toFIGS. 2A and 2B), where the main guideline is to assign the majority oftaper length to where mode transition is most drastic. However sameproblem will still arise that TM is more efficient in terms of couplingyet also suffering high leakage. As a result if during design modeconversion efficiency of TE is guaranteed, redundant taper length willbe required for TM coupling which ultimately builds up considerableleakage loss. As mode is localized very close to Si substrate at thisstage, TM becomes more susceptible to leakage which requires cautiousdesign.

FIG. 7, right side, represents a design in which a mode sorter was usedto determine where the TM and TE crossover occurs. The lengths of the TEand TM segments can be set individually. For example, the TE segment canbe longer to provide reduced coupling loss.

Some examples herein offer more balanced results for both polarization.One group of examples is to divide the main body of the taper into TMand TE part. As shown in FIG. 7, right side, the Si taper becomes 4section piecewise linear. Assigning longer taper length to TE transitionthan TM can get more balanced mode conversion loss.

FIGS. 8A and 8B show another group of examples, in which only one of N2and Si is tapering at any given location along the left-to-right axis.An alternative method is to taper down the intermediate dual SiN widthto delocalize the mode for better evanescent coupling. However releasingthe trapped mode is detrimental for TM since TM leakage will be evenhigher. However, TM mode suffers less mode transition loss andscattering loss than TE mode.

In FIGS. 8A and 8B, for the TM portion of the Si taper, wider SiNwaveguides permit leakage to remain low. There is a short bufferingstage immediately after TM window, mode delocalization at dual SiNwaveguides will have no more effect on TM leakage. Although TE leakagebecomes higher, evanescent coupling also becomes much easier. Withparameters shown in FIGS. 8A and 8B, both polarization has about 0.13 dBmode conversion efficiency and 0.15 dB leakage.

When the N2 width is 500 nm, TM is transferred more effectively to Sithan TE. However, TE generally remains in the waveguide. Tapering N2narrower squeezes TE out to the silicon. This can permit one coupler tooperate efficiently for both TE and TM. In some examples, using a widerN2 segment before narrowing to 200 nm reduces optical loss to thesubstrate of the TM modes, compared to narrowing at the beginning (leftend) of the N2 waveguides. This is because the evanescent coupling of TMwaveguide is easier than the same for TE, but this can increase leakageloss. FIGS. 6A and 6B manage those losses to provide effective TE and TMcoupling.

Scattering loss for SiN parts can be negligible while for Si taper whileSi taper scattering loss is around 0.2 dB for 5 nm σ_(RMS) sidewallroughness. Combing fiber coupling loss, mode transition loss, scatteringas well as leakage, total fiber-to-chip loss is around 1.1 dB for bothpolarization.

In an example of FIG. 8A, With Lsi1=50 μm=LSi3 and LSiTM=100μm=Lbuffer=LSiTE, both TE and TM show ˜0.13 dB mode conversion loss and˜0.15 dB leakage. Stage 3 can couple light from the intermediate SiN(e.g., N2) to Si inverse taper (e.g., S0). In some examples, TE couplingis less efficient than TM but TM leakage is higher than TE. Therefore,in some of these examples, the waveguides are shaped to more rapidlycouple TM into Si but let TE stay in SiN during that process. In anexample of FIG. 8A, TM transition occurs at 120 nm-170 nm Si widthexpansion (TM window) and TE at 170 nm-230 nm (TE window). A short TMtaper first couples TM light into Si, where leakage will be relativelysmall. Tapering down the width of dual intermediate SiN waveguides torelease the TE mode enhances evanescent coupling for TE, but mayincrease TE leakage. Therefore, a TE taper in Si is used to absorb theremaining TE portion of incident light.

In an example, scattering loss for SiN waveguides can be negligible. Insome examples, scattering loss of an Si taper with a 5 nm σ_(RMS)sidewall roughness, scattering loss can be ˜0.2 dB for TE and negligiblefor TM. For 250 μm-long stage 1, 600 μm stage 2, and 400 μm stage 3,mode conversion efficiency can be ≥˜93%. Thus total mode transition lossafter three stages can be ˜0.31 dB.

In view of the foregoing, various aspects provide an optical couplerthat can, e.g., effectively couple optical energy between a single-modeoptical fiber and a silicon waveguide on an integrated circuit (IC). Atechnical effect is to gradually expand or contract the mode fielddiameter, depending on the direction of propagation.

FIG. 23 is a high-level diagram showing the components of an exampledata-processing system 2301 for analyzing data and performing otheranalyses described herein, and related components. The system 2301includes a processor 2386, a peripheral system 2320, a user interfacesystem 2330, and a data storage system 2340. The peripheral system 2320,the user interface system 2330, and the data storage system 2340 arecommunicatively connected to the processor 2386. Processor 2386 can becommunicatively connected to network 2350 (shown in phantom), e.g., theInternet or a leased line, as discussed below. Systems 2301 and 2302 caneach include one or more optical couplers as described herein, or one ormore of systems 2386, 2320, 2330, 2340, and can each connect to one ormore network(s) 2350. Processor 2386, and other processing devicesdescribed herein, can each include one or more microprocessors,microcontrollers, field-programmable gate arrays (FPGAs),application-specific integrated circuits (ASICs), programmable logicdevices (PLDs), programmable logic arrays (PLAs), programmable arraylogic devices (PALs), or digital signal processors (DSPs).

Processor 2386 can implement processes of various aspects describedherein. Processor 2386 and related components can, e.g., carry outprocesses for transmitting or receiving data by optical-electronicconversion. For example, processor 2386 can operate a photodiode toreceive data via an optical coupler as described herein, or can operatea laser diode to transmit data via an optical coupler as describedherein.

Processor 2386 can be or include one or more device(s) for automaticallyoperating on data, e.g., a central processing unit (CPU),microcontroller (MCU), desktop computer, laptop computer, mainframecomputer, personal digital assistant, digital camera, cellular phone,smartphone, or any other device for processing data, managing data, orhandling data, whether implemented with electrical, magnetic, optical,biological components, or otherwise.

The phrase “communicatively connected” includes any type of connection,wired or wireless, for communicating data between devices or processors.These devices or processors can be located in physical proximity or not.For example, subsystems such as peripheral system 2320, user interfacesystem 2330, and data storage system 2340 are shown separately from theprocessor 2386 but can be stored completely or partially within theprocessor 2386.

The peripheral system 2320 can include or be communicatively connectedwith one or more devices configured or otherwise adapted to providedigital content records to the processor 2386 or to take action inresponse to processor 186. For example, the peripheral system 2320 caninclude digital still cameras, digital video cameras, cellular phones,or other data processors. The processor 2386, upon receipt of digitalcontent records from a device in the peripheral system 2320, can storesuch digital content records in the data storage system 2340.

The user interface system 2330 can convey information in eitherdirection, or in both directions, between a user 2338 and the processor2386 or other components of system 2301. The user interface system 2330can include a mouse, a keyboard, another computer (connected, e.g., viaa network or a null-modem cable), or any device or combination ofdevices from which data is input to the processor 2386. The userinterface system 2330 also can include a display device, aprocessor-accessible memory, or any device or combination of devices towhich data is output by the processor 2386. The user interface system2330 and the data storage system 2340 can share a processor-accessiblememory.

In various aspects, processor 2386 includes or is connected tocommunication interface 2315 that is coupled via network link 2316(shown in phantom) to network 2350. For example, communication interface2315 can include an integrated services digital network (ISDN) terminaladapter or a modem to communicate data via a telephone line; a networkinterface to communicate data via a local-area network (LAN), e.g., anEthernet LAN, or wide-area network (WAN); or a radio to communicate datavia a wireless link, e.g., WIFI or GSM. Communication interface 2315sends and receives electrical, electromagnetic, or optical signals thatcarry digital or analog data streams representing various types ofinformation across network link 2316 to network 2350. Network link 2316can be connected to network 2350 via a switch, gateway, hub, router, orother networking device.

In various aspects, system 2301 can communicate, e.g., via network 2350,with a data processing system 2302, which can include the same types ofcomponents as system 2301 but is not required to be identical thereto.Systems 2301, 2302 can be communicatively connected via the network2350. Each system 2301, 2302 can execute computer program instructionsto transmit or receive data optically.

Processor 2386 can send messages and receive data, including programcode, through network 2350, network link 2316, and communicationinterface 2315. For example, a server can store requested code for anapplication program (e.g., a JAVA applet) on a tangible non-volatilecomputer-readable storage medium to which it is connected. The servercan retrieve the code from the medium and transmit it through network2350 to communication interface 2315. The received code can be executedby processor 2386 as it is received, or stored in data storage system2340 for later execution.

Data storage system 2340 can include or be communicatively connectedwith one or more processor-accessible memories configured or otherwiseadapted to store information. The memories can be, e.g., within achassis or as parts of a distributed system. The phrase“processor-accessible memory” is intended to include any data storagedevice to or from which processor 2386 can transfer data (usingappropriate components of peripheral system 2320), whether volatile ornonvolatile; removable or fixed; electronic, magnetic, optical,chemical, mechanical, or otherwise. Example processor-accessiblememories include but are not limited to: registers, floppy disks, harddisks, tapes, bar codes, Compact Discs, DVDs, read-only memories (ROM),erasable programmable read-only memories (EPROM, EEPROM, or Flash), andrandom-access memories (RAMs). One of the processor-accessible memoriesin the data storage system 2340 can be a tangible non-transitorycomputer-readable storage medium, i.e., a non-transitory device orarticle of manufacture that participates in storing instructions thatcan be provided to processor 2386 for execution.

In an example, data storage system 2340 includes code memory 2341, e.g.,a RAM, and disk 2343, e.g., a tangible computer-readable rotationalstorage device or medium such as a hard drive. Computer programinstructions are read into code memory 2341 from disk 2343. Processor2386 then executes one or more sequences of the computer programinstructions loaded into code memory 2341, as a result performingprocess steps described herein. In this way, processor 2386 carries outa computer implemented process. For example, steps of methods describedherein, blocks of the flowchart illustrations or block diagrams herein,and combinations of those, can be implemented by computer programinstructions. Code memory 2341 can also store data, or can store onlycode.

Various aspects herein may be embodied as computer program productsincluding computer readable program code (“program code”) stored on acomputer readable medium, e.g., a tangible non-transitory computerstorage medium or a communication medium. A computer storage medium caninclude tangible storage units such as volatile memory, nonvolatilememory, or other persistent or auxiliary computer storage media,removable and non-removable computer storage media implemented in anymethod or technology for storage of information such ascomputer-readable instructions, data structures, program modules, orother data. A computer storage medium can be manufactured as isconventional for such articles, e.g., by pressing a CD-ROM orelectronically writing data into a Flash memory. In contrast to computerstorage media, communication media may embody computer-readableinstructions, data structures, program modules, or other data in amodulated data signal, such as a carrier wave or other transmissionmechanism. As defined herein, computer storage media do not includecommunication media. That is, computer storage media do not includecommunications media consisting solely of a modulated data signal, acarrier wave, or a propagated signal, per se.

The program code includes computer program instructions that can beloaded into processor 2386 (and possibly also other processors), andthat, when loaded into processor 2386, cause functions, acts, oroperational steps of various aspects herein to be performed by processor2386 (or other processor). Computer program code for carrying outoperations for various aspects described herein may be written in anycombination of one or more programming language(s), and can be loadedfrom disk 2343 into code memory 2341 for execution. The program code mayexecute, e.g., entirely on processor 2386, partly on processor 2386 andpartly on a remote computer connected to network 2350, or entirely onthe remote computer.

In some examples, peripheral system 2320 can include or be connected toat least one optical or electronic active unit 2322 (“opto/elec activeunit”). The active unit 2322 can include, e.g., at least one of any ofthe following optical components or electronic components: lenses,mirrors, or gratings; microelectromechanical systems (MEMS) devices orstructures such as movable micromirrors, resonators, or oscillators;photodiodes, photomultiplier circuits (solid-state, tube, or otherwise),or other optical-to-electronic conversion devices; light-emitting diodes(LEDs); lasers such as in-plane, vertically-emitting, or other laserdiodes, or other semiconductor lasers, solid, liquid, or gas lasers, orother electronic-to-optical conversion devices.

In some examples, a peripheral system 2320 can include or be connectedto at least one coupler 2324, e.g., as discussed herein with referenceto FIG. 1-8B or 24-27.

In some examples, the coupler 2324 can be connected to an optical fiber2326, e.g., via a connector 2328. Connector 2328 can include, e.g., ascrew or snap connector such as an FC, LC, or MIC connector. A splicecan be used in addition to or instead of connector 2328. In theillustrated example, optical fiber 2326 can be a networking fibercommunicatively connected to system 2302, but this is not limiting. Insome examples, the coupler 2324 can be connected to an optical fiber2326 via a splice. For example, the coupler 2324 can be arranged at afacet 2712 and a cleaved end of optical fiber 2326 can be butted upagainst the facet 2712 or otherwise disposed proximal to facet 2712.

Coupler 2324 can convey light (electromagnetic fields) between opticalfiber 2326 and active unit 2322, e.g., light transmitted from system2301, light transmitted to system 2301, or light in either direction.

FIG. 24 shows an example waveguide coupler. Axes are as in FIG. 5. Insome examples, evanescent coupling is more efficient when the mode isaligned with Si taper structure than when it is not aligned. Forexample, a longer taper length may be required if the mode is misalignedwith Si taper. The larger the position offset between the mode and theSi taper (coupling distance), the lower the evanescent couplingefficiency (evanescent field falls off exponentially). Therefore, theexample shown (only two waveguides) may have coupling loss. Bycomparison, adding an intermediate coupling step to split one-stepevanescent coupling process into two or more steps, e.g., as in FIGS. 2Aand 5, can reduce evanescent coupling loss.

FIG. 25 shows an example Si waveguide, e.g., in the S0 layer and in theL2 region shown in FIGS. 2A and 2B. The example waveguide uses apiecewise-linear taper where L2b covers the majority of the modetransition. In this example, TM coupling is more efficient than TE. Forexample, with a 400 μm-long total L2, TM efficiency can be ˜100% and TEmode transition efficiency can be ˜99%. The piecewise-linear taper canperform more effectively than a single linear taper. In some examples,the waveguide is a total of 500 μm long, providing TE and TMefficiencies >98%.

FIG. 26 shows simulation results of a configuration similar to thatshown in FIGS. 6A and 6B. Axes and notation are as discussed herein withreference to FIG. 3.

FIG. 27 shows an axonometric drawing showing internal components of asilicon photonic device 2700, e.g., an integrated circuit (IC), andrelated components. The example of FIG. 27 is similar to the exampleshown in FIG. 2B. However, for clarity of the drawing, FIG. 27 does notshow the waveguide tapers shown in FIG. 2B. Instead, the waveguides aredepicted as rectangular prisms. Moreover, the N2 waveguide 2720 reachesfacet 2712 in FIG. 27, but the similar N2 waveguide in FIG. 2B does notreach the facet (which is in the −Z direction from L0). In someexamples, waveguide 2720 reaches facet 2712 and has a tapered segmentbeginning substantially at facet 2712. Throughout FIG. 27, dotted linesare used to show spatial relationships, and do not themselves representcomponents. Other layers can be present in device 2700 other than thoseshown here. For example, other layers can be applied over upper claddinglayer 2710, discussed below. X, Y, and Z axes are shown with dash-dotarrows and are as in FIGS. 2A, 2B, 4A, and 5-8B. The depicted componentscan constitute the entirety of an IC, or only a portion thereof. Forexample, layers 2702-2710 can extend beyond the boundaries depicted.

Device 2700 includes substrate 2702, e.g., Si or another semiconductor.A plurality of layers is arranged over the substrate 2702, e.g., in astack. The layers include cladding layer 2704 (e.g., BOX), lowercladding layer 2706 (e.g., SiO₂), intermediate cladding layer 2708(e.g., SiO₂), and upper cladding layer 2710 (e.g., SiO₂). The claddinglayers 2706,2708, and 2710 can be part of a lower waveguide assembly(e.g., S0), an intermediate waveguide assembly (e.g., N2), and an upperwaveguide assembly (e.g., N1), respectively.

The layers are configured to define a facet 2712 at an edge of thedevice 2700. The facet 2712 can include a portion of the edge of thedevice 2700. Additionally or alternatively, the facet 2712 can includean indentation, protrusion, or other structure. Facet 2712 is capable ofexchanging light

The layers are also configured to define an optical coupler 2714extending away from the facet 2712 at least in a longitudinal direction2716, e.g., into the IC. For example, direction 2716 can besubstantially normal to facet 2712. In some examples, longitudinaldirection 2716 is the Z axis shown in FIGS. 2A-4A and 5-22. The opticalcoupler 2714 can include a plurality of waveguides, each at least partlyencapsulated within a corresponding cladding layer. In some examples,each waveguide has a higher refractive index than any of the claddinglayer(s) within which it is at least partly encapsulated.

In the illustrated example, lower waveguide 2718 (e.g., Si) isencapsulated within lower cladding layer 2706 (S0). Lower waveguide 2718does not reach facet 2712. A dotted box extending from lower waveguide2718 shows more clearly how lower waveguide 2718 is arranged withinlayer 2706. The end of lower waveguide 2718 closest to facet 2712 isdepicted as a hatched quadrilateral.

Intermediate waveguide 2720 is encapsulated within intermediate claddinglayer 2708 (N2). Upper waveguides 2722, 2724, and 2726 are encapsulatedwithin upper cladding layer 2710 (N1). Lower waveguide 2718 extendsfarther from the facet 2712 in the longitudinal direction 2716 than doesa second waveguide of the plurality of waveguides. The second waveguidecan be, e.g., intermediate waveguide 2720 or any of the upper waveguides2722, 2724, and 2726. Moreover, any of those choices for the secondwaveguide is located farther above the substrate 2702 than is the lowerwaveguide 2718. This arrangement, using dimensions selected as describedherein based on the wavelength of light to be coupled, permits lightincident on facet 2712 to be effectively coupled to lower waveguide2718, which can then provide the light to active unit 2322. Additionallyor alternatively, light produced by active unit 2322 can be effectivelycoupled from lower waveguide 2718 out to facet 2712, from which it canbe received by a lens, fiber, or other optical system. An example isshown in phantom of fiber 2728 butt-spliced with facet 2712.

In some examples, fiber 2728 can be retained by a V-groove (omitted forclarity of the drawing). For example, fiber 2728 can be held in aV-groove of a V-groove array, e.g., made of PYREX, optical glass, oranother glass, or quartz, silicon or another crystalline solid. TheV-groove or V-groove array can be retained in position with respect todevice 2700, e.g., using optically-clear adhesive (OCA), index-matchedadhesive, mechanical retention features such as clips or braces, orother retaining features.

In some examples, device 2700 can include multiple assemblies such asthat shown. Each assembly can include, e.g., facet 2712 and opticalcoupler 2714, or facet 2712, optical coupler 2714, and active unit2322). The assemblies can be arranged along one edge of an IC ormultiple edges, or any combination thereof. For example, multiple copiesof the components shown can be included in the IC, spaced apart alongthe X axis. Accordingly, the depicted axes are not limiting, and anyedge of an IC can be used to form optical couplers and other structuresshown. In some examples, n couplers are arranged along one edge, and ann-groove V-groove array is retained in position with respect to the ncouplers so that n fibers are spliced or otherwise aligned to respectivecouplers of the n couplers. E.g., n=10.

As discussed herein, the arrangement of waveguides at facet 2712 permitseffectively receiving the mode from the fiber with increased tolerancefor misalignment compared to prior schemes. Therefore, optical couplers2714 and devices 2700 as described herein can be used with passivealignment of individual fibers or fiber arrays (e.g., V-groove arrays).Couplers herein can therefore reduce the need for active alignment offibers or arrays.

In some examples, facet 2712 can receive a free-space signal, e.g.,light focused by a lens or other optics on to the facet 2712. In someexamples, facet 2712 can emit a free-space signal to be received byanother optical component, e.g., another device 2700. Accordingly, insome examples, device(s) 2700 can be used for free-space orfiber-mediated optical communication or power transfer, e.g.,chip-to-chip communication or power transfer.

Illustrative Examples

Some examples include at least one of features 1-8, below.

1. An edge coupler for SMF28 or other single-mode fiber. The fiber inputcan be designed as multi-layer format where mode is coupled down to Silayer via intermediate layer(s).

2. Three layers: one Si, two nitride (or other dielectric).

3. Two nitride layers forming a matrix.

4. An intermediate layer to permit evanescent coupling to be moreefficient (require less taper length for the same coupling performance)than direct coupling without intermediate layer.

5. A silicon nitride tip array or matrix deployed at facet to captureinput mode. With tip matrix especially, mode can be tailored to increaseoverlap to a mode in the single-mode fiber.

6. A multi-layer taper embedded in oxide and including a thick buriedoxide layer to reduce the leakage (towards Si substrate) while modecoupling down to Si taper.

7. A BOX layer 3 μm thick, or ≥2 μm thick.

8. A taper designed with distinct TE and TM sections to balanceperformance for both polarization.

In some examples, to design a coupler according to some examples herein,the TE and TM transition windows can be found separately, e.g., based onthe material properties or design rules of the silicon process. Atransition window is a range of waveguide width expansions during whichTE or TM (respectively) mode evolutions can occur and the mode areachanges most steeply, e.g., 10%-90% or 20%-80% of the transition. Forexample, for TM, a relatively wider N2 waveguide can be used compared toTE, so that the evanescent field and the leakage shrink. For TE, anarrow N2 waveguide can be used. Therefore, a coupler can be designedthat first uses wider confinement waveguide to hold the mode during TMcoupling in order to reduce leakage, then, farther along the length ofthe waveguide, tapers down the confinement waveguide and starts TE modecoupling with relaxed coupling challenge. In some examples, the TEsection is longer to fully utilize the TE transition window. As notedherein, the coupler is bidirectional in some examples. Therefore, lightemitted by active unit 2322 can transfer TE fields closer to active unit2322, then TM fields farther from active unit 2322. After the TE region,width of suspended waveguide can be decreased, as in FIGS. 8A-8B.

Some examples include one or more of, including any combination of anynumber of, features AA-AM, below. As used herein, references to“dielectric” can additionally or alternatively refer to other materialsthat have relatively low absorption loss in the wavelength bands ofinterest, e.g., <10% or <1%. References to “dielectric” can additionallyor alternatively refer to TiN, polymers, or other substances having ahigher index of refraction than the insulating layer (e.g., the SiO₂),e.g., ≤1% higher, ≤5% higher, ≤10% higher, ≤20% higher, about 40%higher, ≤40% higher, ≤50% higher, or ≤100% higher. Similarly, referencesherein to silicon dioxide (SiO2) can additionally or alternatively referto silicon oxides with different numbers of Si and O atoms per molecule.References to SiO2 can additionally or alternatively refer to polymershaving refractive indexes similar to that of silicon dioxide (e.g., ±5%,±10%, or ±25%). References herein to silicon nitride (SiN) canadditionally or alternatively refer to silicon nitrides with differentnumbers of Si and N atoms per molecule. References herein to siliconnitride (SiN) can additionally or alternatively refer to polymers havingrefractive indexes similar to that of silicon nitride (e.g., ±5%, ±10%,or ±25%). In features AA-AM, parenthetical remarks are for example andexplanation, and are not limiting. Parenthetical remarks given in thisIllustrative Examples section with respect to specific language apply tocorresponding language throughout this section, unless otherwiseindicated.

AA: An optical coupler (e.g., FIG. 2-8B or 25-27), comprising: asemiconductor substrate; an insulating layer (e.g., BOX) arranged overthe semiconductor substrate; and a plurality of waveguide assembliesarranged in a stack (e.g., FIGS. 2A and 2B, left side) over theinsulating layer. Each waveguide assembly can include a waveguide andinsulator or dielectric at least partly encapsulating the waveguide,e.g., N1, N2, N1U, N1M, N1L, or S0. The plurality of waveguideassemblies can include: a semiconductor waveguide assembly (S0, FIG. 2A,2B, 5, or 7) arranged over the insulating layer and comprising a taperedsemiconductor waveguide (e.g., dark waveguide in FIGS. 2A, 2B, 4; centerwaveguide in FIGS. 7-8B) at least partly encapsulated in an associatedinsulating layer (e.g., SiO2); at least one intermediate waveguideassembly (SiN/SiO2 assemblies N1, N1{U,M,L}, N2) arranged over apreceding waveguide assembly of the plurality of waveguide assemblies,each intermediate waveguide assembly comprising at least one dielectricwaveguide (e.g., SiN or other dielectric) at least partly encapsulatedin an associated insulating layer (e.g., SiO2); and an upper waveguideassembly (e.g., N1, FIGS. 2A and 2B, or N1U, FIGS. 6A and 6B) arrangedover an uppermost of the at least one intermediate waveguide assembly,the upper waveguide assembly comprising at least two dielectricwaveguides spaced apart laterally, each of the at least two dielectricwaveguides at least partly encapsulated in an associated insulatinglayer (e.g., SiO2).

AB: The optical coupler according to paragraph AA, wherein (at least oneof the following, in any combination): the semiconductor substratecomprises monocrystalline silicon; the insulating layer comprises buriedoxide (e.g., buried silicon oxide or other semiconductor oxide, orsimilar-index polymer); the associated insulating layers comprisesilicon oxide; or the dielectric waveguides comprise silicon nitride(or, e.g., other nitrides, or similar-index polymer).

AC: The optical coupler according to paragraph AA or AB, furthercomprising an active unit (e.g., active unit 2322, FIG. 23) opticallyconnected with the semiconductor waveguide (Si in assembly S0).

AD: The optical coupler according to any of paragraphs AA-AC, whereinthe at least one intermediate waveguide assembly comprises at least: afirst intermediate waveguide assembly (e.g., N2) comprising at most twodielectric waveguides; and a second intermediate waveguide assemblyarranged over the first intermediate waveguide assembly (e.g., N1 orN1L) and comprising at least three dielectric waveguides.

AE: The optical coupler according to any of paragraphs AA-AD, whereinthe at least one intermediate waveguide assembly comprises at least twointermediate waveguide assemblies (e.g., at least two of N1{U,M,L}),each comprising at least three dielectric waveguides.

AF: The optical coupler according to any of paragraphs AA-AE, wherein atleast one of the at least two dielectric waveguides tapers along alength of the at least one of the at least two dielectric waveguides(e.g., as shown in N1U, FIGS. 6A and 6B: each of the four waveguidesshown in N1U tapers from wider to narrow while moving left to rightacross the figure).

AG: The optical coupler according to any of paragraphs AA-AF, wherein atleast a first waveguide of the at least two dielectric waveguidesapproaches at least a second waveguide of the at least two dielectricwaveguides along a length of the first waveguide (e.g., as shown in N1U,FIGS. 6A and 6B: each of the four waveguides shown in N1U is arranged sothat the separation between the four waveguides reduces while movingleft to right across the figure, and the same is true of the waveguidesin N1M, N1L).

AH: The optical coupler according to any of paragraphs AA-AG, wherein atleast one of the semiconductor waveguide or the dielectric waveguidescomprises at least two taper sections having respective, different ratesof width taper as a function of distance along a longitudinal axis ofthe at least one of the semiconductor waveguide or the dielectricwaveguides (e.g., FIG. 7 for the semiconductor waveguide, or FIGS. 8A-8Bfor both the semiconductor waveguide and the dielectric waveguides).

AI: The optical coupler according to any of paragraphs AA-AH, wherein:(e.g., as in FIG. 8A) the semiconductor waveguide comprises a firsttaper section, followed by a first non-taper section, followed by asecond taper section along a longitudinal axis (dashed line) of thesemiconductor waveguide; the at least one intermediate waveguideassembly comprises a first intermediate waveguide assembly arranged overthe semiconductor waveguide assembly and comprising a first dielectricwaveguide; the first dielectric waveguide comprises a second non-tapersection, followed by a third taper section, followed by a thirdnon-taper section along a longitudinal axis (dotted line) of the firstdielectric waveguide; the first taper section and the second non-tapersection are intersected by a first line (dash-dot line) substantiallyperpendicular to the longitudinal axis (dashed line) of thesemiconductor waveguide; the first non-taper section and the third tapersection are intersected by a second line (dash-dot line) substantiallyparallel to the first line and spaced apart from the first line; and thesecond taper section and the third non-taper section are intersected bya third line (dash-dot line) substantially parallel to the first lineand spaced apart from the first line and from the second line. (Thelocations of the lines in FIG. 8A are for example and are not limiting.)

AJ. A method comprising manufacturing a coupler according to any ofclaims AA-AI using silicon wafer processing steps.

AK. A device comprising: optical coupler(s) according to any of claimsAA-AI; and active unit(s) operatively coupled to respective opticalcoupler(s).

AL. The device according to paragraph AK, further comprising a processoroperatively coupled to the active unit(s) to at least transmit orreceive data.

AM. The device according to paragraph AK or AL, the optical coupler(s)comprising a plurality of the optical couplers.

Further Illustrative Examples

Various examples include one or more of, including any combination ofany number of, the following example features. Throughout these clauses,parenthetical remarks are for example and explanation, and are notlimiting. Other examples of such features may be given throughout thisapplication. Parenthetical remarks given in this Further IllustrativeExamples section with respect to specific language apply tocorresponding language throughout this document, unless otherwiseindicated. Various examples additionally include one or more of,including any combination of any number of, the features listed in the“Illustrative Examples” section above.

A: An optical coupler (e.g., coupler 2324 or 2700, or as in FIG. 2A, 2B,4A, 5-8B, 26, or 27), comprising: a semiconductor substrate (e.g., an Sior III-V substrate, or substrate 2702; a first cladding layer (e.g.,BOX, or layer 2704) arranged over the semiconductor substrate and havinga relatively lower refractive index; and a plurality of waveguideassemblies (e.g., S0, N1, N1U, N1M, N1L, N2, or assemblies includingcladding layers 2706, 2708, or 2710) arranged in a stack over the firstcladding layer, the plurality of waveguide assemblies comprising: alower waveguide assembly arranged over the first cladding layer andcomprising: a lower cladding layer (e.g., 2706) having a relativelylower refractive index; and a tapered lower waveguide (e.g., Siwaveguide in layer S0, or waveguide 2718) at least partly encapsulatedin the lower cladding layer and having a relatively higher refractiveindex; at least one intermediate waveguide assembly (e.g., N2, N1L, orN1M) arranged over a preceding waveguide assembly of the plurality ofwaveguide assemblies, each intermediate waveguide assembly comprising: arespective cladding layer (e.g., layer 2708) having a relatively lowerrefractive index; and at least one intermediate waveguide (e.g., ahigh-index waveguide) (e.g., waveguide 2720) (e.g., the single waveguidein layer N2, FIG. 2B, the two waveguides in layer N2, FIG. 5, or thefour waveguides in each of layers N1L and N1M, FIG. 5) at least partlyencapsulated in the respective cladding layer and having a relativelyhigher refractive index; and an upper waveguide assembly (e.g., N1, FIG.2B, or N1U, FIG. 5) arranged over an uppermost of the at least oneintermediate waveguide assembly, the upper waveguide assemblycomprising: an upper cladding layer having a relatively lower refractiveindex; and at least two (e.g., three in FIG. 2B; four in FIG. 5) upperwaveguides (e.g., waveguides 2722, 2724, and 2726) spaced apartlaterally (e.g., within the cladding layer), each of the at least twoupper waveguides at least partly encapsulated in the upper claddinglayer (e.g., layer 2710) and having a relatively higher refractive index(e.g., the refractive index of each waveguide being higher than therefractive indices of any waveguide(s) that contact or at least partlyencapsulate that waveguide).

B: The optical coupler according to paragraph A, wherein: thesemiconductor substrate comprises crystalline silicon or a III-Vsemiconductor; the first cladding layer comprises buried oxide; therespective cladding layers of the at least one intermediate waveguideassembly comprise silicon oxide; the intermediate waveguide comprisessilicon nitride; or the at least two upper waveguides comprise siliconnitride.

C: The optical coupler according to paragraph A or B, further comprisingan active unit (e.g., an optoelectronic device or other device asdiscussed herein with reference to active unit 2322) connected with thelower waveguide (e.g., waveguide 2718).

D: The optical coupler according to any of paragraphs A-C, wherein theat least one intermediate waveguide assembly comprises at least: a firstintermediate waveguide assembly (e.g., N2, FIG. 5) comprising at mosttwo intermediate waveguides of the corresponding at least oneintermediate waveguide; and a second intermediate waveguide assembly(e.g., N1L, FIG. 5) arranged over the first intermediate waveguideassembly and comprising at least three intermediate waveguides of thecorresponding at least one intermediate waveguide.

E: The optical coupler according to any of paragraphs A-D, wherein theat least one intermediate waveguide assembly comprises at least twointermediate waveguide assemblies (e.g., N1L and N1M, FIG. 5), eachcomprising at least three intermediate waveguides of the correspondingat least one intermediate waveguide.

F: The optical coupler according to any of paragraphs A-E, wherein atleast a first waveguide of the at least one intermediate waveguide or ofthe at least two upper waveguides tapers along a length of the firstwaveguide (e.g., waveguide 2720; see taper in: FIG. 2B, waveguide inlayer N2; FIG. 6A, waveguides in L1; FIGS. 8A and 8B: outer waveguides;FIG. 25).

G: The optical coupler according to any of paragraphs A-F, wherein atleast a first waveguide of the at least one intermediate waveguide or ofthe at least two upper waveguides approaches at least a second waveguideof the at least two intermediate waveguides or of the at least two upperwaveguides along a length of the first waveguide (e.g., FIG. 2B, in the“L0” region of the N1 layer; or FIG. 6A, 6B, or 26, L1, bottom).

H: The optical coupler according to any of paragraphs A-G, wherein atleast a first waveguide of the lower waveguide, the at least oneintermediate waveguide, or the at least two upper waveguides comprisesat least two taper sections having respective, different rates of widthtaper as a function of distance along a longitudinal axis of the firstwaveguide (e.g., the N2 waveguide in FIG. 2B; the rightmost waveguide inFIG. 4A; the center waveguides in FIG. 7; the waveguides in FIG. 8A; thetop-center waveguides or the bottom three waveguides in FIG. 8B; or thewaveguide in FIG. 25).

I: The optical coupler (e.g., as in example feature AI, above) accordingto any of paragraphs A-H, wherein: the lower waveguide comprises a firsttaper section, followed by a first non-taper section, followed by asecond taper section along a longitudinal axis of the lower waveguide(e.g., FIG. 8A, S0 waveguide; FIG. 8B, bottom S0 waveguide); the atleast one intermediate waveguide assembly comprises a first intermediatewaveguide assembly arranged over the lower waveguide assembly andcomprising a first intermediate waveguide; the first intermediatewaveguide comprises a second non-taper section, followed by a thirdtaper section, followed by a third non-taper section along alongitudinal axis of the first intermediate waveguide; the first tapersection and the second non-taper section are intersected by a first linesubstantially perpendicular to the longitudinal axis of the lowerwaveguide; the first non-taper section and the third taper section areintersected by a second line substantially parallel to the first lineand spaced apart from the first line; and the second taper section andthe third non-taper section are intersected by a third linesubstantially parallel to the first line and spaced apart from the firstline and from the second line.

J: The optical coupler according to any of paragraphs A-I, wherein thelower waveguide (e.g., Si) has a higher index of refraction than atleast one of the intermediate waveguides (e.g., SiN).

K: An integrated circuit (e.g., SOI) comprising: a substrate (e.g.,FIGS. 2A, 2B, 5: Si substrate; FIG. 24: bottom layer; FIG. 27 #2702); aplurality of layers (e.g., other layers in FIGS. 2A, 2B, 5, and 24; FIG.27 #2704, 2706, 2708, 2710, 2718, 2720, 2722, 2724, 2726) arranged overthe substrate and configured to define: a facet (e.g., FIG. 27 #2712) atan edge of the integrated circuit; and an optical coupler (e.g., coupler2324 or 2714, or as in FIG. 2A, 2B, 4A, 5-8B, 26, or 27) extending awayfrom the facet at least in a longitudinal direction (e.g., the Z axis);wherein: the optical coupler comprises a plurality of waveguides (e.g.,FIGS. 2A, 2B, 4A, 5-8B, 24-26: Si, SiN, and other waveguides, e.g., inN1, N1U, N1M, N1L, N2, or S0 layers; FIG. 27 #2718, 2720, 2722, 2724),each at least partly encapsulated within a corresponding cladding layer(e.g., FIGS. 2A, 2B, 4A, 5-8B, 24-26: SiO₂ and other cladding layers,e.g., in N1, N1U, N1M, N1L, N2, S0, or BOX layers; FIG. 27 #2704, 2706,2708, 2710); a first waveguide (e.g., S0 waveguides; FIG. 27 #2718) ofthe plurality of waveguides extends farther from the facet in thelongitudinal direction than does a second waveguide (e.g., N1, N1U, N1M,N1L, or N2 waveguides; FIG. 27 #2720, 2722, 2724, or 2726) of theplurality of waveguides; and the second waveguide is located fartherabove the silicon substrate than is the first waveguide.

L: The integrated circuit according to paragraph K, wherein thewaveguides of the plurality of waveguides have higher refractive indicesthan the corresponding cladding layers (e.g., in FIG. 2B, the Siwaveguide has a higher index than the SiO₂ S0 layer and than the BOXlayer; or in FIG. 27, #2718 has a higher index than #2706; #2720 than#2708; or all of #2722, 2724, and 2726 than #2710) (e.g., each waveguidecan have a higher index than the highest index of any of the claddinglayers it touches or in which it is at least partly encapsulated).

M: The integrated circuit according to paragraph K or L, furthercomprising an active unit (e.g., a photodiode or semiconductor laser)(e.g., FIGS. 23 and 27 #2322) arranged over the substrate, wherein theoptical coupler (e.g., #2714) is disposed at least partly between (e.g.,along the longitudinal axis, e.g., the Z axis) the facet (e.g., #2712)and the active unit (e.g., FIG. 27 #2322).

N: The device according to paragraph M, further comprising a processor(e.g., FIG. 23 #2386) operatively coupled to the active unit(s) to atleast transmit or receive data.

O: The device according to paragraph M or N, wherein: the device furthercomprises a plurality of active units, the plurality of active unitscomprising the active unit; the plurality of layers are furtherconfigured to define: a plurality of facets at the edge of theintegrated circuit, the plurality of facets comprising the facet; and aplurality of optical couplers disposed at least partly betweenrespective facets of the plurality of facets and respective active unitsof the plurality of active units, the plurality of optical couplerscomprising the optical coupler; each optical coupler of the plurality ofoptical couplers defines a respective longitudinal axis; and eachoptical coupler of the plurality of optical couplers comprises: a firstwaveguide arranged relatively closer to the respective active unit inthe longitudinal direction and relatively closer to the substrate; and asecond waveguide arranged relatively farther from the respective activeunit in the longitudinal direction and relatively farther from to thesubstrate (e.g., multiple copies of the components shown in FIG. 27,arranged along the X axis).

P: The device according to paragraph O, wherein: the plurality of layerscomprises a first layer (e.g., S0 or N2) and a second layer (e.g., N2 orN1, respectively); the first layer is arranged at least partly betweenthe substrate and the second layer; the respective first waveguides ofthe plurality of optical couplers are arranged in the first layer; andthe respective second waveguides of the plurality of optical couplersare arranged in the second layer (e.g., multiple couplers on a singledie, the couplers sharing a common layer arrangement or stackup) (e.g.,in FIG. 27, the first layer can be #2706, the first waveguides #2718,the second layer #2708, and the second waveguides #2720).

Q: An assembly comprising: a semiconductor photonic device having: asubstrate; a plurality of facets (e.g., FIG. 27 #2712 or the faces shownin FIG. 2A, 2B, 5, or 24); and a plurality of optical couplers (e.g.,coupler 2324 or 2700, or as in FIG. 2A, 2B, 4A, 5-8B, 26, or 27)associated with respective facets of the plurality of facets; and aplurality of single-mode optical fibers (e.g., FIG. 27 #2728) (or, e.g.,fibers of other types, e.g., multimode or polarization-maintaining)disposed in a splice configuration (e.g., butted against or otherwise asdiscussed herein near the discussion of connector 2328, or with respectto FIG. 27) with respect to respective facets of the plurality offacets; wherein each optical coupler of the plurality of opticalcouplers comprises means for coupling an electromagnetic field incidenton the facet towards the substrate as the electromagnetic field proceedsinto the semiconductor photonic device (e.g., an emitter or receiver oflight).

R: The assembly according to paragraph Q, further comprising a V-groovearray (e.g., as discussed herein with reference to FIG. 27) configuredto retain the single-mode optical fibers in position with respect to therespective facets.

S: The assembly according to paragraph Q or R, wherein each opticalcoupler comprises: a respective first waveguide (e.g., S0, or FIG. 27#2718) disposed over the substrate; and a respective second waveguide(e.g., N1 or N2, or FIG. 27 #2720-2726) disposed over the substrate, therespective second waveguide being farther from the substrate than therespective first waveguide and extending closer to the respective facetthan the respective first waveguide.

T: The assembly according to paragraph S, wherein each optical couplerfurther comprises a respective third waveguide (e.g., FIGS. 2A-2B anytwo of the N1 waveguides; FIG. 5 either waveguide in N2, or any three ofthe N1U, N1M, or N1L waveguides; FIG. 27 any two of #2722-2726) disposedin a common layer with the respective second waveguide and laterallyspaced apart from the respective second waveguide.

U: The assembly according to paragraph S or T, wherein the respectivefirst waveguides and the respective second waveguides: are at leastpartly encapsulated in corresponding cladding layers; and haverespective indices of refraction that are higher than respective indicesof refraction of the corresponding cladding layers (e.g., as in featureL, above).

Conclusion

The operations of the example processes are illustrated in individualblocks and summarized with reference to those blocks. The processes areillustrated as logical flows of blocks, each block of which canrepresent one or more operations that can be implemented in hardware,software, or a combination thereof. In the context of software, theoperations represent computer-executable instructions stored on one ormore computer-readable media that, when executed by one or moreprocessors, enable the one or more processors to perform the recitedoperations. Generally, computer-executable instructions includeroutines, programs, objects, modules, components, data structures, andthe like that perform particular functions or implement particularabstract data types. The order in which the operations are described isnot intended to be construed as a limitation, and any number of thedescribed operations can be executed in any order, combined in anyorder, subdivided into multiple sub-operations, or executed in parallelto implement the described processes. The described processes can beperformed by resources associated with one or more computing systems2301, 2302 or processors 2386, such as one or more internal or externalCPUs or GPUs, or one or more pieces of hardware logic such as FPGAs,DSPs, or other types of accelerators.

The methods and processes described above can be embodied in, and fullyautomated via, software code modules executed by one or more generalpurpose computers or processors. The code modules can be stored in anytype of computer-readable storage medium or other computer storagemedium. Some or all of the methods can alternatively be embodied inspecialized computer hardware. For example, various aspects herein maytake the form of an entirely hardware aspect, an entirely softwareaspect (including firmware, resident software, micro-code, etc.), or anaspect combining software and hardware aspects These aspects can allgenerally be referred to herein as a “service,” “circuit,” “circuitry,”“module,” or “system.”

Conditional language such as, among others, “can,” “could,” “might” or“may,” unless specifically stated otherwise, are understood within thecontext to present that certain examples include, while other examplesdo not include, certain features, elements or steps. Thus, suchconditional language is not generally intended to imply that certainfeatures, elements or steps are in any way required for one or moreexamples or that one or more examples necessarily include logic fordeciding, with or without user input or prompting, whether certainfeatures, elements or steps are included or are to be performed in anyparticular example. The word “or” and the phrase “and/or” are usedherein in an inclusive sense unless specifically stated otherwise.Accordingly, conjunctive language such as, but not limited to, at leastone of the phrases “X, Y, or Z,” “at least X, Y, or Z,” “at least one ofX, Y or Z,” and/or any of those phrases with “and/or” substituted for“or,” unless specifically stated otherwise, is to be understood assignifying that an item, term, etc., can be either X, Y, or Z, or acombination of any elements thereof (e.g., a combination of XY, XZ, YZ,and/or XYZ). As used herein, language such as “one or more Xs” shall beconsidered synonymous with “at least one X” unless otherwise expresslyspecified. Any recitation of “one or more Xs” signifies that thedescribed steps, operations, structures, or other features may, e.g.,include, or be performed with respect to, exactly one X, or a pluralityof Xs, in various examples, and that the described subject matteroperates regardless of the number of Xs present.

Although some features and examples herein have been described inlanguage specific to structural features or methodological steps, it isto be understood that the subject matter herein is not necessarilylimited to the specific features or steps described. Any processdescriptions, elements or blocks in the flow diagrams described hereinor depicted in the attached figs should be understood as potentiallyrepresenting modules, segments, or portions of code that include one ormore executable instructions for implementing specific logical functionsor elements in the process. Alternate implementations are includedwithin the scope of the examples described herein in which elements orfunctions can be deleted, or executed out of order from that shown ordiscussed, including substantially synchronously or in reverse order,depending on the functionality involved as would be understood by thoseskilled in the art. It should be emphasized that many variations andmodifications can be made to the above-described examples, the elementsof which are to be understood as being among other acceptable examples.All such modifications and variations are intended to be included hereinwithin the scope of this disclosure and protected by the followingclaims. Moreover, in the claims, any reference to a group of itemsprovided by a preceding claim clause is a reference to at least some ofthe items in the group of items, unless specifically stated otherwise.

What is claimed is:
 1. An optical coupler, comprising: a semiconductorsubstrate; a first cladding layer arranged over the semiconductorsubstrate and having a relatively lower refractive index; and aplurality of waveguide assemblies stacked vertically over the firstcladding layer, the plurality of waveguide assemblies comprising: alower waveguide assembly arranged over the first cladding layer andcomprising: a lower cladding layer having a relatively lower refractiveindex; and a tapered lower waveguide being at least partly encapsulatedin the lower cladding layer and having a relatively higher refractiveindex; a first intermediate waveguide assembly comprising: a firstintermediate cladding layer having a relatively lower refractive index;and two first intermediate waveguides spaced laterally from each other,each of the first intermediate waveguides being at least partlyencapsulated in the first intermediate cladding layer and having arelatively higher refractive index; and an upper waveguide assemblyarranged over the first intermediate waveguide assembly, the upperwaveguide assembly comprising: an upper cladding layer having arelatively lower refractive index, the upper cladding layer having asmaller extent vertically than does the first intermediate claddinglayer; and at least two upper waveguides spaced laterally from eachother, each of the at least two upper waveguides being at least partlyencapsulated in the upper cladding layer and having a relatively higherrefractive index.
 2. The optical coupler according to claim 1, wherein:the semiconductor substrate comprises crystalline silicon or a III Vsemiconductor; the first cladding layer comprises buried oxide; thefirst intermediate cladding layer comprises silicon oxide; each of thetwo first intermediate waveguides comprises silicon nitride; or the atleast two upper waveguides comprise silicon nitride.
 3. The opticalcoupler according to claim 1, further comprising an active unitconnected with the lower waveguide.
 4. The optical coupler according toclaim 1, further comprising: a second intermediate waveguide assemblybeing disposed vertically between the upper waveguide assembly and thefirst intermediate waveguide assembly and comprising: a secondintermediate cladding layer; and at least four second intermediatewaveguides spaced apart laterally from each other and at least partlyencapsulated in the second intermediate cladding layer; and a thirdintermediate waveguide assembly being disposed vertically between theupper waveguide assembly and the second intermediate waveguide assemblyand comprising: a third intermediate cladding layer; and at least fourthird intermediate waveguides spaced apart laterally from each other andat least partly encapsulated in the third intermediate cladding layer,wherein the upper waveguide assembly comprises at least four upperwaveguides spaced apart laterally from each other.
 5. The opticalcoupler according to claim 1, wherein at least a first waveguide of thefirst intermediate waveguides or of the upper waveguides tapers along alength of the first waveguide.
 6. The optical coupler according to claim1, wherein at least a first waveguide of the first intermediatewaveguides or of the upper waveguides approaches at least a secondwaveguide of the first intermediate waveguides or of the upperwaveguides along a length of the first waveguide.
 7. The optical coupleraccording to claim 1, wherein at least a first waveguide of the lowerwaveguide, the first intermediate waveguides, or the upper waveguidescomprises at least two taper sections having respective, different ratesof width taper as a function of distance along a longitudinal axis ofthe first waveguide.
 8. The optical coupler according to claim 1,wherein: the lower waveguide comprises a first taper section, followedby a first non-taper section, followed by a second taper section along alongitudinal axis of the lower waveguide; each of the first intermediatewaveguides comprises a second non-taper section, followed by a thirdtaper section, followed by a third non-taper section along alongitudinal axis of the first intermediate waveguide; the first tapersection and the second non-taper section are intersected by a first linesubstantially perpendicular to the longitudinal axis of the lowerwaveguide; the first non-taper section and the third taper section areintersected by a second line substantially parallel to the first lineand spaced apart from the first line; and the second taper section andthe third non-taper section are intersected by a third linesubstantially parallel to the first line and spaced apart from the firstline and from the second line.
 9. The optical coupler according to claim1, wherein the lower waveguide has a higher index of refraction than atleast one of the first intermediate waveguides.
 10. An integratedcircuit comprising: the optical coupler of claim 1, the optical couplerbeing configured to define a facet at an edge of the integrated circuit,the optical coupler extending away from the facet at least in alongitudinal direction.
 11. The integrated circuit according to claim10, further comprising an active unit arranged over the substrate,wherein the plurality of waveguide assemblies is disposed at leastpartly between the facet and the active unit.
 12. The integrated circuitaccording to claim 11, wherein: the device further comprises a pluralityof active units, the plurality of active units comprising the activeunit; the device further comprises a plurality of optical couplersincluding the optical coupler; the plurality of waveguide assemblies isfurther configured to define: a plurality of facets at the edge of theintegrated circuit, the plurality of facets comprising the facet; and aplurality of optical couplers disposed at least partly betweenrespective facets of the plurality of facets and respective active unitsof the plurality of active units, the plurality of optical couplerscomprising the optical coupler; and each optical coupler of theplurality of optical couplers defines a respective longitudinal axis.13. The optical coupler according to claim 1, wherein: the firstcladding layer comprises a buried oxide layer, each of the lowercladding layer, the first intermediate cladding layer, and the uppercladding layer comprises silicon oxide, the tapered lower waveguidecomprises silicon, and the upper waveguides and the first intermediatewaveguides comprise silicon nitride.
 14. The optical coupler accordingto claim 1, wherein the at least two upper waveguides comprise threetapered waveguides.
 15. The optical coupler according to claim 1,further comprising: a second intermediate waveguide assembly beingdisposed vertically between the upper waveguide assembly and the firstintermediate waveguide assembly and comprising: a second intermediatecladding layer; and at least three second intermediate waveguides spacedapart laterally from each other and at least partly encapsulated in thesecond intermediate cladding layer, wherein the upper waveguide assemblycomprises at least three upper waveguides spaced apart laterally fromeach other.
 16. The optical coupler according to claim 1, wherein: theat least two upper waveguides extend from a facet in a longitudinaldirection, the tapered lower waveguide is spaced apart from the facet inthe longitudinal direction, and the two first intermediate waveguidesare spaced apart from the facet in the longitudinal direction.
 17. Theoptical coupler according to claim 1, further comprising: a matrix ofwaveguide tips configured to receive incident radiation, the matrix ofwaveguide tips comprising three rows of four waveguides, wherein thethree rows are stacked vertically, the waveguides in each of the rowsare laterally spaced apart from each other, and one of the rows of fourwaveguides comprises the at least two upper waveguides.
 18. The opticalcoupler according to claim 4, wherein each of the second intermediatecladding layer and the third intermediate cladding layer has a shortervertical thickness than the first intermediate cladding layer.
 19. Anoptical coupler, comprising: a semiconductor substrate; a buried oxidelayer disposed above the semiconductor substrate; and a plurality ofwaveguide assemblies stacked in a vertical direction above the firstcladding layer, the plurality of waveguide assemblies comprising: alower waveguide assembly comprising: a lower cladding layer; and atapered lower waveguide at least partly encapsulated in the lowercladding layer and having a higher refractive index than the lowercladding layer and the first cladding layer; a first intermediatewaveguide assembly comprising: a first intermediate cladding layer; andtwo first intermediate waveguides at least partly encapsulated in thefirst intermediate cladding layer, and having a higher refractive indexthan the intermediate cladding layer; an upper waveguide assemblycomprising: an upper cladding layer having a narrower vertical thicknessthan the first intermediate cladding layer; and four upper waveguidesspaced apart from each other in the lateral direction and at leastpartly encapsulated in the upper cladding layer, the upper waveguideshaving a higher refractive index than the upper cladding layer; and asecond intermediate waveguide assembly disposed between the firstintermediate waveguide assembly and the upper waveguide assembly, thesecond intermediate waveguide assembly comprising: a second intermediatecladding layer having a narrower vertical thickness than the firstintermediate cladding layer; and four second intermediate waveguidesspaced apart from each other in the lateral direction, at least partlyencapsulated in the second intermediate cladding layer, and aligned withthe four upper waveguides in the vertical direction, the secondintermediate waveguides having a higher refractive index than the secondintermediate cladding layer.